Magnetic Random Access Memory (MRAM) is a nonvolatile memory having a TMR element using a magnetoresistive effect (Tunneling Magneto Resistive: TMR) and has integration density similar to Dynamic Random Access Memory (DRAM) and a high speed performance similar to Static Random Access Memory (SRAM), and the world pays attention to MRAM as a revolutionary next-generation memory in which data is rewritten repeatedly.
The TMR element basically has a magnetization resistance effect film provided between an upper electrode and a lower electrode and having a tunnel barrier layer sandwiched between a magnetization fixing layer (hereinafter also referred to as a “pin layer”) and a magnetization free layer (hereinafter also referred to as a “free layer”) and is located at an intersection between a word line and a bit line used in reading and writing signals. The TMR element is used as a memory cell when the upper electrode and the lower electrode of the TMR element are connected to wiring.
When a current flows into the TMR element, the current vertically flows from the lower electrode to the upper electrode. A level of an electric resistance value of a current flowing through an insulating layer is changed between “0” and “1” by freely changing the direction of the magnetization of the magnetization free layer which is a ferromagnetic layer, and information is exchanged with metal wiring, whereby a signal is read or written.
An ion beam etching (hereinafter also referred to as “IBE”) technique is used as a method of processing the TMR element. In the IBE, an electrical power is supplied to a discharge portion to generate a plasma, and, thus, to draw ions from the plasma through application of voltage to a grid, whereby an ion beam is formed. The ion beam enters a substrate and mainly physically etches a material on the substrate.
In the process for producing the TMR element, a magnetoresistive effect film formed on a substrate is processed by various etching methods such as IBE, reactive ion etching (hereinafter also referred to as “RIE”), and reactive IBE and isolated into individual TMR elements. When the magnetoresistive effect film is processed in accordance with a pattern, an etched material is partially physically etched and scattered from the substrate. The scattered etched material is partially adhered again to a side wall of the TMR element and deposited thereon. When the re-deposited film is adhered to a side wall of the tunnel barrier layer, the magnetization fixing layer and the magnetization free layer are short-circuited by the re-deposited film, so that the function as the TMR element is lost.
Patent Literature 1 discloses a technique of, in the element isolation of the TMR element, forming, in a stepwise manner, an insulating layer on a side wall exposed by etching to form an insulating layer on the side surface before adhesion of a re-deposited film, and, thus, to prevent short-circuiting of the TMR element due to the re-deposited film.